THE DEEP CONNEXIONS OF THE CEEEBKAL NERVES. 595 



hypoglossal pass between the main inferior olivary nucleus and the medial accessory 

 olivary nucleus, and many of them on their way to the surface pierce the ventral 

 lamina of the main olivary nucleus. 



No decussation between the nerves of opposite sides takes place in the medulla 

 oblongata, but commissural fibres pass between the two nuclei (Kolliker). Further, 

 numerous fibres from the opposite pyramidal tract enter the nucleus and end in connexion 

 with its cells. The nucleus is thus brought into connexion with the motor area of the 

 opposite side of the cerebral cortex. 



Nervus Accessorius. The accessory nerve also is a motor nerve, and it is 

 generally described as consisting of a spinal and a cerebral or accessory part. 



The spinal part of the nerve emerges by a series of roots which issue from the 

 surface of the lateral column of the superior part of the spinal medulla as low down 

 as the fifth cervical nerve. These take origin in a column of cells situated in the 

 anterior column of gray matter of the spinal medulla, close to its lateral margin, and 



Fasciculus gracilis Fasciculus cuneatus 



_ > 



ANT.K 



FIG. 528. DIAGRAM OP THE SPINAL 

 ORIGIN OF THE ACCESSORY NERVE 

 (after Bruce). 



Entering 

 posterior nerve 

 root 



Substantia 

 gelatinosa 



Emerging 

 filum of 

 accessory nerve 

 Fibres of spinal 



rigin of 

 accessory 

 Emerging 



,nterior nerve- 

 root 



FIG. 529. SECTION THROUGH THE SUPERIOR PART OF THE 



CERVICAL REGION OF THE SPINAL MEDULLA (Orang). 

 Showing the origin of the spinal part of the accessory nerve. 



immediately behind the nerve-cells which give rise to the fibres of the anterior 

 roots of the upper five cervical nerves. The cells of the accessory nucleus are 

 large, multipolar, and in every respect similar to the motor cells of the spinal 

 nerves. The axons from these cells leave the dorsal aspect of the nucleus in 

 converging groups to form the fila radicularia or root-bundles of the nerve. These, 

 in the first place, proceed straight backwards in the anterior column of gray matter. 

 Reaching the bay between the two columns of gray matter, they turn sharply 

 laterally into the white matter and traverse the lateral funiculus to gain their 

 points of exit from the spinal medulla. At the decussation of the pyramids, fila, 

 which join the accessory nerve, are seen to proceed from the detached head of the 

 anterior column of gray matter. 



The cerebral part of the accessory nerve has its nucleus of origin in the medulla 

 oblongata ; and its fila, as they proceed laterally from this, can be distinguished 

 by the fact that they pursue a course on the ventral side of the tractus spinalis 

 of the trigeminal nerve, whereas the vagus roots, with which they are apt to be 

 confused, pass through or lie on the dorsal aspect of the trigeminal root (Kolliker). 

 The nucleus of origin of the cerebral part of the accessory nerve is formed by the 

 same column of cells which constitutes the nucleus ambiguus, and which, at a higher 

 level, gives motor fibres to the vagus and glossopharyngeal nerves. 



The part of the accessory nerve which takes origin in the spinal medulla supplies the 

 sterno-mastoid and trapezius muscles. The cerebral portion joins the vagus, and through the 

 external laryngeal and recurrent nerves it supplies the muscles of the larynx. The portion of 



39 (i 



